i have done some research on this problem the past few days and a visit to the JY. so my 98 4.0l lerado with manual temp controls is having a problem i noticed about four days ago when i stopped for some pizza and come back and the heater was running still. i played with the knobs and it turned off by turning the motor off by the knob. i couldn't get it to do it again that night. then the next day my girl drove it and had mentioned the heater was staying on with the key out. i checked it out a little showed her what i had figured out with turning it off but also found out i could change the speeds to the blower motor with no key in the ignition. it had drained the battery that night. didn't find that out till the next day. today i figured it was the controls in the dash so some time at the junkyard i pulled one for a 96(not the right one by the way and didn't find out till i had the mine out) i pulled the control unit apart and found a relay inside. so a trip to the parts house i found a relay and replaced it and put things back together and still having the same issue. so i don't wake up to a dead battery i pulled the blow motor fuse. anyone have some incite? dose this sound like the resistor has gone bad?